Lubricants for continuous metal-casting operations

ABSTRACT

The invention relates to synthetic lubricants used at very high temperatures in the process of continuous casting of molten metals. The lubricants are applied as a liquid film to the surfaces of the molds into which the metal is poured. In continuous casting of steel the molten steel is poured into an open-bottomed mold of the desired product shape. The steel is cooled in the mold just enough to harden the exterior surface of the casting, which forms a shell or container that holds the balance of the liquid metal. The inner walls of the mold are continuously coated with a liquid lubricant as the metal is poured therein. The partially solidified casting is then continuously withdrawn from the bottom of the mold, where it is further cooled by water sprays until all the metal is solidified. The casting is cut as it descends through the equipment into desired lengths. The polyol esters of fatty acids having 12 to 22 carbon atoms, or mixtures thereof, are excellent lubricants for molds used in continuous casting of metals. The preferred polyols have two to 12 hydroxy groups and at least five carbon atoms, including for example, pentaerythritol or polymers thereof, trimethylol ethane, trimethylol propane, and glycols containing from two to 40 carbon atoms. Also included in these polyols are inositol, mannitol, sorbitol, glucose, sucrose, trimethylol benzene, hexamethylol benzene, methyl glucosides, polyglycerols and, in fact, any polyol capable of reacting with at least two selected fatty acid molecules to form a minimum of a diester.

United States Patent [72] inventors 541 LUBRICANTS Fort (10111 11913605 METAL-- CASTING OPERATIONS 7 Claims, No Drawings [52] U.S. Cl 164/73, 252/56 S [51] Int. Cl C10m H26 [50] Field of Search 252/56, 56 S; l17/5.1, 5.3; 164/73, 268

[56] References Cited UNITED STATES PATENTS 2,837,791 6/1958 Tessmann 164/73 X 3,034,186 5/1962 Holshouser... 164/73 X 3,446,267 5/1969 Gricol et a1. 164/268 OTHER REFERENCES Barnes et al., Lubrication Engineering, Aug. 1957, pp. 454- 458.

Kirk-Othmer, Encyclopedia of Chem. TechnoL, Vol. 13 (1954)pg. 575.

Hilditch et al., The Chemical Constitution of Natural Fats, 4

m Edn. 1964) pp. 298- 299.

Primary Examiner -Daniel E. Wyman Assistant ExaminerW. Cannon Attorney-Joseph Rossman ABSTRACT: The invention relates to synthetic lubricants used at very high temperatures in the process of continuous casting of molten metals. The lubricants are applied as a liquid film to the surfaces of the molds into which the metal is poured. in continuous casting of steel the molten steel is poured into an open-bottomed mold of the desired product shape. The steel is cooled in the mold just enough to harden the exterior surface of the casting, which forms a shell or container that holds the balance of the liquid metal. The inner walls of the mold are continuously coated with a liquid lubricant as the metal is poured therein. The partially solidified casting is then continuously withdrawn from the bottom of the mold, where it is further cooled by water sprays until all the metal is solidified. The casting is cut as it descends through the equipment into desired lengths.

The polyol esters of fatty acids having 12 to 22 carbon atoms, or mixtures thereof, are excellent lubricants for molds used in continuous casting of metals. The preferred polyols have two to 12 hydroxy groups and at least five carbon atoms, including for example, pentaerythritol or polymers thereof, trimethylol ethane, trimethylol propane, and glycols containing from two to 40 carbon atoms. Also included in these polyols are inositol, mannitol, sorbitol, glucose, sucrose. trimethylol benzene, hexamethylol benzene, methyl glucosides, polyglycerols and, in fact, any polyol capable of reacting with at least two selected fatty acid molecules to form a minimum ofa diester.

LUBRICANTS FOR CONTINUOUS METAL-CASTING OPERATIONS This application is a continuation-in-part of application Ser. No. 734,572, filed June 5, l968 now US. Pat. No. 3,526,596 Sept. 1, 1970.

This invention relates to the use of certain chemical compositions as mold lubricants in the continuous casting of molten metals. More specifically, the invention is particularly useful in the lubrication of water-cooled copper molds used in the continuous casting of steel. However, the compositions are.

also useful as mold lubricants for other metals and alloys such as brass, steel alloys, bronze, aluminum, silver and others.

The process for continuous casting of steel generally com prises the following steps, although the precise order may be changed:

l. Steel is melted in a furnace.

2. The molten steel is poured into a ladle.

3. The molten steel is then tapped into a vessel called a tundish.

4. The molten metal is then cast continuously into a watercooled copper mold which oscillates in a vertical plane to aid in releasing continuously a billet or slab. A lubricant is continuously supplied to the interior walls of the copper mold. At this temperature 2,700-2,800 F.) the lubricant decomposes into vapors and possibly carbonaceous matter. These decomposition products have sufficient duration of existence at this temperature to act as parting compositions between the copper mold wall and the steel. There has to be sufficient heat exchange to form a solid skin on the billet or slab sufiiciently strong not to break out" and cause molten metal to spill when the bar or billet or slab moves below the copper mold to the secondary cooling area. The product and decomposition products must burn away or decompose completely so as not to increase the carbon content of the steel. The surface of the moving steel piece must be free of spots, inclusions or pits caused by excessive residence time of the lubricant or its decomposition products. The decomposition vapors may not be noxious or poisonous so that mill personnel in the area are not poisoned or made ill. The lubricant must leave the copper mold with a minimum of varnish" or other coating so that the operation may proceed continuously without interruption to clean the mold. Such residues will give rise to surface blemishes which must be removed later mechanically with loss of yield and at high labor cost.

The lubricants of this invention may be used in any type of mold equipment used for continuous casting of steel, whether the straight mold, vertical discharge type, the straight mold with bending rolls, or the curved mold type. Such equipment is described in Continuous Casting of Steel" published 1965 as Special Report 89 by The Iron and Steel Institute, London, England, and also in Continuous and Pressure Casting" published 1964 by the Association of Iron and Steel Engineers, Pittsburgh, Pa.

MOLD LUBRICATION Successful continuous casting of steel depends on the proper combination of many operating factors but none is more essential than lubrication of the mold. The continuous casting process is unique in the steel industry because without continuous and reliable lubrication of the mold walls, the process slows down or stops. Thus, when production rates are so dependent upon lubrication practices, they are placed in a position of importance which they do not normally occupy. The most important lubrication problem in continuous casting of metals is the lubrication of the mold surfaces to prevent sticking" in the mold. A continuous constant film of lubricant is necessary to allow consistent heat transfer from the metal strand to the mold surface.

The purposes of lubricating the mold walls are:

1. To prevent sticking in the mold.

2. To aid heat transfer in the mold.

3. To aid in avoiding scum pickup on the surface of the solidifying strand.

The lubricant is an important factor in phenomena of solidification at the wall interface. As the molten metal comes into contact with the sides of the cooler mold walls, rapid heat transfer occurs resulting in the formation of a very thin skin which becomes thicker at a progressively reducing rate, depending upon the thermal conductivity of the steel and the mold material, and the temperature differential. The prevention of ruptures or cracks in the solidified skin is most important.

Proper lubrication of the mold walls is but one of the many factors influencing skin formation. Some others are:

l. Mold wall surface condition (smooth, rough, etc.

2. Mold taper design.

3. Mold reciprocating speed.

4. Rate of withdrawal.

5. Temperatures of mold and hot metal.

The greatest operating problem in lubricating in the continuous casting mold is to maintain uniform, consistent oil delivery. Since quantities used are minute-on the order of l pound of oil per ton of steel-flow rates are very small and oil pressures are low. On one 60X6 inch slab installation, flow requirements are 0.25 pints of oil per minute to each of 24 lubricating points around the periphery. Mechanical design of the lubricating system has two major areas 1 a divider block for accurate control of the oil flow to each orifice and (2) an orifice opening in the mold wall which will generate an oil film of about 0.001 inch uniformly distributed.

The oil film is created by slits in the mold wall, about 0.020 inch high, widths to suit, through which the oil runs down the inside of the mold wall. Oil is supplied to the slits from a well inside and mold wall, which in turn is connected to the oil source through a divider block. The oil supply to each point is precisely controlled.

The following compositions have been previously suggested as lubricants for the mold in continuous casting of steel and all have one or more serious deficiencies.

Rapeseed Oil Crude or Refined This natural product is subject to acrolein formation in decomposition with lachrymatory effects and choking of mill personnel. These oils are susceptible to oxidation on standing and formation of a rancid" product which contributes to other problems. Varnishing" occurs frequently with these products.

Rapeseed Oil-Air Blown This viscous product shows the inherent difficulties of rapeseed oil in addition to the lack of manageability of flow through the orifices in the copper mold and to the orifices in cold climates.

Mineral Oils When used cause intense smoke development and burn far too readily. The excess smoke precludes operational visibility above the mold, a necessity for proper operation of the system.

Low Viscosity, Low Molecular Weight Polyisobutylenes These products require large application because of their great volatility and ease of depolymerization. It should be mentioned that decomposition products which are low in molecular weight and are hydrocarbon in nature, tend to burn almost explosively giving the rise to soot and large flames. Vegetable Oils:

Castor oil-causes varnishing of the mold and gives rise to acrolein.

Cottonseed Oilsame as castor oil.

Soybean Oilsame as castor oil.

In addition, all of these natural products are subject to the usual ebb and flow of supply in a fatand oil-poor world. Molten Slag and Glass These are effective mold release agents but remain embedded in the steel surface requiring subsequent scarfing to remove the solids. In addition, delivery of the slag or glass to the appropriate location involves complex mechanisms.

We have found that the compositions described in our copending application 734,572, filed June 5, 1968, overcome virtually all of these difficulties. These products do not decomlow in viscosity to flow readily and by appropriate choice of 5 composition have pour points well below 0 F. for use in cold climates.

DESCRIPTION OF PREFERRED EMBODIMENTS The following compositions are very effective lubricants in continuous casting of steel and other molten metals. The polyol esters of fatty acids having 12 to 22 carbon atoms, or mixtures thereof, are excellent lubricants for metal-casting operations. The preferred polyols have two to 12 hydroxy groups and at least five carbon atoms, including for example, pentaerythritol or polymers thereof, trimethylol ethane, trimethylol propane, and glycols containing from two to 40 carbon atoms. Also included in these polyols are inositol, mannitol, sorbitol, glucose, sucrose, trimethylol benzene, hexamethylol benzene, methyl glucosides, polyglycerols and, in fact, any polyol capable of reacting with at least two selected fatty acid molecules to form a minimum of a diester.

Among the fatty acids useful for making the polyol esters are:

a. Natural fatty acids both saturated and unsaturated con taining 12 to 22 carbon atoms including the following acids:

Laurie Margaric Licanic Lauroleic Stearic Elaeo-stearic Myristic Oleic Docosenoic Myristoleic Linoleic Docosapolyenoic Arachidic Eicoscnoic Tallow fatty acids which are mixtures Eicosapolyenoic Behcnic of saturated and unsaturated fatty Penladecanoic Linoleic acids having l6 to 18 carbon Palmitic Ricinoleic atoms Palmitoleic Dihydroxyl Tall oils stearic Also included are any isomers of the above acids such as elaidic acid. Any of these acids may be used in admixture to obtain the desired esters. Smaller amounts of rosin acids may also be used along with the fatty acids. Neoacids or isoacids, such as neopentanoic, neodecanoic, neotridecanoic acids and other similar acids obtainable from oxidation of oxo processes compounds are also included in this group. Those acids obtainable by oxidation of alpha olefines and alphaolefinsderived alcohols are also useful. Finally, synthetic fatty acids obtainable from petroleum products as well as so-called naphthenic acids may be used.

The esters of the fatty acids and polyol may be prepared by any known procedure commonly used for preparation of these esters. These include heating in a still by direct thermal fusion, with and without catalysts. Such catalysts may be acids, Lewistype acids, metallic oxides, metallic hydroxides, and the like. The water of the reaction is then suitably removed. Azeotropic removal of water of reaction, distillation of water of reaction under vacuum, and removal of water of reaction, distillation of water of reaction under vacuum, and removal of water of reaction by gas sparging may be used. The ester products are used directly in anhydrous condition as lubricants. Mixture of esters may also be used.

The following are specific illustrative examples particularly useful as lubricants in continuous casting of steel. The components parts given in the examples are by weight:

EXAMPLE I Tallow fatty acids Trimeth lol ethane 840 parts I20 parts These components were mixed and heated with nitrogen passing through the bottom of a reaction flask to remove water of reaction. Temperatures of 500-525 F. were used with agitation of the reaction mixture. When about 54 parts of water had been removed the reaction was stopped. The product was brown liquid consisting essentially of tritallowate of trimethylol ethane.

K EXAMPLE 2 Oleic ucid 1.]20 parts Pentaerythritol I36 part1 Toluene Sulfonic Acid 0.] parts Xylene 50 parts This mixture was heated at temperatures of up to 400 F. while water of reaction was distilled ofi azeotropically, the xylene layer being returned continuously. Wen 70 parts of water of reaction had been removed, the xylene was evaporated in vacuo leaving a yellow liquid product which was essentially tetraoleate of pentaerythritol.

EXAMPLE 3 Tall oil-distilled 855 parts Trimethylol propane I35 parts Boron trifluoride etherate 0.l parts EXAMPLE 4 Red oil(oleic acid) Polyethylene glycol P-toluene sulfonic acid oil parts 560 parts 600 parts This mixture was heated at 325 F. until 35 parts of water of reaction had been removed. A light brown oily liquid resulted which was essentially polyethylene glycol dioleate.

EXAMPLE 5 .000 3.... 254 parts Coconut fatty acids Dipentaerythritol This mixture was heated at 525 F. until -90 parts of water of reaction had been removed. The reaction product was a somewhat viscous yellow brown liquid which was essentially the ester of dipentaerythritol and coconut fatty acids.

ADVANTAGES OF lNVENTlON The lubricants of the present invention meet the requirements for successful mold lubrication in continuous casting of steel which were previously discussed. The lubricants have the following characteristics:

l.l Viscosity-The lubricants are capable of being pumped readily through the small application nozzles or openings in the copper mold.

2. Pour Point-The lubricants have a relatively low pour point to eliminate the need of preheating the oil for use.

3. Water-FreeThe lubricants are water free and also are water rejecting at high humidities. Under the reducing conditions of molten steel Fe+l-l,O-FeO+l-l the formation of hydrogen is most deleterious to the steel.

4. Smoke and Fumes-At the elevated temperatures of molten steel, fumes are formed rapidly. These fumes are white or gray and do not conceal the mold as badly as smoke.

We claim:

1. in a process of continuous casting of steel which comprises the steps of pouring molten metal at a temperature of about 2,700 to 2,800 F. into an open-bottomed mold of suitable shape, continuously supplying a constant film of lubricant to the inner surfaces of said mold, cooling the steel in the mold sufficiently to harden the exterior surface of the metal to form a partially solidified casting which retains the molten metal in the interior shape, continuously withdrawing the partially solidified casting from the bottom of the mold, and further cooling the casting until it is solidified, wherein the improvement consists in supplying to the inner surfaces of said mold a lubricant consisting essentially of a polyester of a polyol and a 4. In a process as defined in claim 1, wherein the lubricant is tetraoleate of pentaerythritol.

5. In a process as defined in claim I, wherein the lubricant is tritallate of trimethylol propane.

6. In a process as defined in claim 1, wherein the lubricant is polyethylene glycol dioleate. 1

7. In a process as defined in claim 1, wherein the lubricant is the polyester of dipentaerythritol and coconut fatty acids.

* i l i l 

2. In a process as defined in claim 1, wherein the lubricant is a polyester of pentaerythritol and a fatty acid having 12 to 22 carton atoms.
 3. In a process as defined in claim 1, wherein the lubricant is tritallowate of trimethylol ethane.
 4. In a process as defined in claim 1, wherein the lubricant is tetraoleate of pentaerythritol.
 5. In a process as defined in claim 1, wherein the lubricant is tritallate of trimethylol propane.
 6. In a process as defined in claim 1, wherein the lubricant is polyethylene glycol dioleate.
 7. In a process as defined in claim 1, wherein the lubricant is the polyester of dipentaerythritol and coconut fatty acids. 